Bloom et al. in U.S. Pat. No. 5,311,360, entitled “Method and Apparatus For Modulating A Light Beam,” teach a grating light valve™ type device which operates in a reflection mode and a diffraction mode. The grating light valve™ type device includes elongated elements suspended above a substrate. In the reflective mode, reflective surfaces of the grating light valve™ type device cause incident light to constructively combine to form reflected light. In the diffractive mode, the reflective surfaces of the grating light valve™ type device are separated by a quarter wavelength of the incident light to produce diffracted light. When the grating light valve™ type device is in the diffractive mode, the grating light valve™ type device predominantly diffracts light into a plus one diffraction order and a minus one diffraction order but also diffracts a small amount of light into higher diffraction orders.
Bloom et al. further teach an alternative grating light valve type device which operates in the reflection mode and in a blazed diffraction mode. The alternative grating light valve type device includes the elongated elements suspended above the substrate. For the alternative grating light valve type device, the elongated elements include off-axis neck portions at ends of each of the elongated elements. In the reflection mode, the elongated elements are parallel, causing incident light to reflect from the elongated elements and, thus, produce the reflected light. In the blazed diffraction mode, each of the elongated elements is rotated about an axis defined by the off-axis neck portions to produce a blazed diffraction.
Because the light modulator is switched between the reflection mode and the blazed diffraction mode and because the reflection mode diffracts small quantities of light into the same angles as does the blazed diffraction mode, a contrast between the non-activated state and the activated state is less than an optimum contrast.
What is needed is a blazed diffractive light modulator which provides higher contrast.